The power of suggestion is very strong, as is the Placebo effect, and BP is right to point out that the power of the mind can affect the body. I have a healthy respect for Herbalism and familiarising oneself with common herbs and poisonous ones is a prudent approach. Where I start to get annoyed are the quacks, charlatans and Snake Oil salesmen who can heal you with mumbo jumbo chanting and a crystal, or even worse a fucking drum circle
The Monastic system had a fantastic lore of Herbal remedies and a well organised garden system in which to grow them. I don't poopoo herbalism at all, just all the attendant new age dross that seems to accompany this subject. Anyway must go, I have a Toad to lick.